Intruder detecting security system

Abstract

This electronic perimeter intruder detecting security system is arranged for measuring the differences of propagation times and/or velocities of a plurality of different seismic-like waves simultaneously set up by an intruder at a plurality of sensor stations and for calculating the location, velocity, and frequently for identifying the type of intruder. Provisions are disclosed for screening false alarms or waves emanating from without a guarded zone and for ignoring waves from sources not of interest in guarding that zone.

The invention claimed is: 
     
       1. An intruder detecting security system for determining an intrusion across a boundary, comprising a plurality of pairs of sensors responsive to waves propagated through geological and like substantially rigid materials with each pair having the sensors arranged operationally orthogonally of each other, and the pairs arranged substantially in line along said boundary,   analyzing circuitry connected to said sensors for determining the difference in the time for longitudinal and transverse waves set up by a single disturbance to travel from the disturbance to said sensors and   computing circuitry connected to said analyzing circuitry for resolving location of said disturbance.   
     
     
       2. An intruder detecting security system as defined in claim 1 and wherein said pairs of sensors are arranged on either side of said line along said boundary with alternate pairs on the same side   for resolving ambiguity of direction of said disturbance with respect to said boundary.   
     
     
       3. An intruder detecting security system as defined in claim 1 and wherein said sensors are geophones.   
     
     
       4. An intruder detecting security system as defined in claim 3 and wherein: said analyzing circuitry comprises band-pass signal amplifying circuitry connected to each sensor and having   a pass band centered about the natural frequency of the sensor.   
     
     
       5. An intruder detecting security system as defined in claim 4 and wherein said pass bandwidth is of the order of twenty percent of said natural frequency.   
     
     
       6. A perimeter intruder detecting security system as defined in claim 2 and wherein said analyzing circuitry comprises ranging circuitry coupled to at least one of said sensor pairs, and   bearing analyzing circuitry coupled to said one sensor pair.   
     
     
       7. A perimeter intruder detecting security system as defined in claim 2 and wherein said analyzing circuitry comprises ranging circuitry coupled to at least two of said sensor pairs, and   said computing circuitry is arranged for determining the location of said disturbance by an arithmetic triangulation process.   
     
     
       8. A perimeter intruder detecting security system as defined in claim 7 and wherein said analyzing circuitry further comprises coupling circuitry arranged for coupling to at least three non-colinear pairs of said sensor pairs, and   said computing circuitry is arranged for resolving any ambiguity in direction by comparing results of said triangulation process.   
     
     
       9. A perimeter intruder detecting security system as defined in claim 2 and wherein said computing circuitry is arranged for ignoring all data outside a predetermined zone.   
     
     
       10. A perimeter intruder detecting security system for determining an intrusion into the area within the perimeter, comprising, a multiple of pairs of sensors responsive to waves propagated through geological and substantially rigid materials with each pair having the sensors arranged operationally orthogonally of each other, and the pairs orientated substantially along radial and tangential lines with respect to a central location within said area,   analyzing circuitry connected to said sensors for determining the difference in the times for a single disturbance about said perimeter to travel by shear and by compression waves set up by that single disturbance, and   computing circuitry connected to said analyzing circuitry for resolving the location of said disturbance by triangulation.   
     
     
       11. A perimeter intruder detecting security system as defined in claim 10 and incorporating further analyzing circuitry connected to said sensors for determining the mass of impact of a single disturbance.   
     
     
       12. A perimeter intruder detecting security system as defined in claim 11 and wherein said further analyzing circuitry comprises peak detecting circuitry.   
     
     
       13. An intruder detecting system for determining an intrusion across a boundary, comprising a plurality of pairs of geophones with each pair having the geophones arranged operationally orthogonally of each other and the pairs located substantially along said boundary,   a plurality of pairs of detector circuits individually coupled to said pairs of geophones and arranged to produce bistatic output signal levels individually in response to activity of the associated geophones,   analyzing circuitry coupled to said pairs of detector circuits for determining data from the different times for pressure and shear waves generated by a single impact to travel from the point of said single impact to said geophones, and   computing circuitry coupled to said analyzing circuitry for resolving said data selectively for presentation and utilization and both.   
     
     
       14. An intruder detecting system for determining an intrusion across a boundary as described in claim 13 and incorporating a band-pass filter circuit interposed between a geophone and the associated detector.   
     
     
       15. An intruder detecting system for determining an intrusion across a boundary as described in claim 14 and wherein said band-pass filter circuit has a band-width of twenty percent of the center frequency, and   said center frequency substantially matches the resonant frequency of the associated geophone.   
     
     
       16. An intruder detecting system for determining an intrusion across a boundary as described in claim 14 and incorporating an electronically variable impedance device shunted across the output terminals of said band-pass filter and having a control terminal, and   an automatic gain controlling circuit connected between said control terminal and the associated detector circuit in the polarity for maintaining the gain of the circuit substantially constant.   
     
     
       17. An intruder detecting system for determining an intrusion across a boundary as described in claim 14 and wherein said detector circuit comprises   a full wave rectifying circuit and a comparator coupled to said band-pass filter circuits, and   a comparator circuit having one input terminals connected to said full-wave rectifying circuit, another input terminals connected to a source of direct potential, and an output terminal,   said comparator circuit being arranged for producing said bistable output signal levels in accordance with the output of said rectifying circuit being respectively less than said direct potential and equal to and greater than said direct potential.   
     
     
       18. An intruder detecting system for determining an intrusion across a boundary as described in claim 13 and wherein said analyzing circuitry comprises gating circuitry coupled to said individual detector circuits and to a source of timing pulses and having output terminals,   exclusive OR gating circuitry connected to the output terminals of said signal gating circuitry and having an output terminal,   a binary flip-flop circuit having an input terminal connected to the output terminal of said XOR gating circuitry, a reset terminal, and two complementary output terminals,   counting circuitry having a count terminal coupled to said source of timing pulses, enabling terminals coupled to one of said output terminals of said flip-flop circuit, and output terminals at which values representing time intervals are presented.   
     
     
       19. An intruder detecting system for determining an intrusion across a boundary as described in claim 18 and incorporating an OR gating circuit interposed between said flip-flop circuit and said enabling terminals and having input and output terminals so connected and an additional input terminal,   an AND gating circuit having one input terminal connected to the output terminal of said XOR gating circuit, another input terminal connected to a potential representing a logical level, and an output terminal connected to said additional terminal of said OR gating circuit,   register circuitry having input terminals connected to the output terminals of said counting circuitry, loading terminals, connected to said source of timing pulse, at least two enabling terminals, and output terminals at which values representing time intervals are presented, and   gating circuitry connected between the other of said output terminals of said flip-flop circuit and one of said enabling terminals of said register circuitry for entering a value in a portion of said register circuitry for entering a value in a portion of said register cicuitry representative of the time between the arrival of the pressure and shear waves from one geophone pair.   
     
     
       20. An intruder detecting system for determining an intrusion across a boundary as described in claim 18 and incorporating And gating circuitry having a plurality of input terminals connected to predetermined output terminals of said counting circuitry and having an output terminal coupled to said reset terminal of said flip-flop circuit.